Pattern comparison of a stack of three five element 20 m Yagi-Uda antennas at different heights: 15 m (50 ft) high (blue), 30 m (100 ft) high (red) and 45 m (150 ft) high (black).

When the antenna at the 15 m (50 ft) level is used, there is a main lobe centered around 18 degrees and a deep null at 45 degrees elevation above the horizon.

When the antenna at the 30 m (100 ft) level is used, there are two main lobes, at 10 and 32 degrees and deep nulls near 20 degrees and 45 degrees of elevation above the horizon.

When the antenna at the 45 m (150 ft) level is used, there are three main lobes at 7, 21 and 36 degrees and deep nulls at 14, 28 and 46 degrees.

This shows that one antenna at one height will not cover all the incoming angles that vary through the day depending on the ionospheric propagation conditions.

Now, let's explore the combinations of selecting two antennas in phase out of a stack of three and also when the three antennas are selected at the same time.

There are four possible combinations when using more than one antenna at the time:

-All three antennnas at the same time (black). Single Lobe at 8 degrees.

-The two at the top (green). Lobes at 7 and 23 degrees, null at 17 degrees.

-The two at the bottom (red). Main lobe at 12 degrees.

-The top antenna and the bottom antenna (blue). Lobes at 8 and 34 degrees. Nulls at 16 and 46 degrees.

The use of the StackMatch to combine the antennas in phase delivers more gain, up to 5 dB over a single antenna when three are used and 3 dB in the case of two antennas compared to a single one. But even more important is the coverage of the angles with the resultant lobes obtained with seven different combinations; the four listed above and the three possibilities when using one of the three antennas.

Low angle lobes are good for long-haul contacts specially at dusk and down while high angle lobes are better near local noon along the propagation path.